"To the detriment of Plaintiff and the putative Class... Defendants' marketing campaign has succeeded," the suit dryly reads.

"Plaintiff would not have paid the price he paid for the iPhone 4S, if he had not seen these representations."

But, says Fazio, he was deeply disappointed when he got his new phone home. When he asked Siri for directions, he says, it either failed to understand or, after a long delay, gave the wrong answer.

"Defendant’s advertisements regarding the Siri feature are fundamentally and designedly false and misleading," he claims.

"Notwithstanding Apple’s extensive multi-million dollar advertising campaign showcasing the Siri feature, and the fact that the iPhone 4S is more expensive than the iPhone 4, the iPhone 4S’s Siri feature does not perform as advertised, rendering the iPhone 4S merely a more expensive iPhone 4."

According to the lawsuit, Apple never made it clear that the scenes depicted in its ads were 'fiction' - and the fact that the company described Siri at the time as a work in progress shows it was aware that it was falling short.

Many users have been complaining on Apple support forums that Siri works only sporadically - or not at all. Resetting all settings appears to work for most, although some complain that this needs doing every few days. Many claim that the service has actually got worse since the November launch, possibly because of increasing strain on the company's servers.

One user suggests changing the feature's name from 'Siri' - to 'Sorry'. But Fazio wants rather more: he's asking for 'compensatory damages, statutory damages, restitution, and all other forms of monetary and non-monetary relief recoverable under California law'.